C5 Flashcards
What is a yield of a product?
The mass of the product that is made in a chemical process
What is theoretical yield?
The maximum amount of mass that is possible to be made from the given mass of reactants
How do you calculate theoretical yield?
Basically a reacting masses question:
1. From mass find mols
2. Find mols of desired thing through stoichometry
3. Convert back from mols to mass
Will be answered in grams
How do you calculate percentage Yield?
(Actual yield ➗theoretical yield)✖️100
What affects percentage yield? (!100%)
🟢transfer loss of substance
🟢reaction may not go to completion
🟢reaction may react in a different way than planned
What is atom economy?
How many atoms in the reactants form a desired product
How do you calculate atom economy?
(Sum of Mr of desired products➗sum of Mr of all products)✖️100
BALANCING NUMBERS ARE INCLUDED
What factors affect the reaction pathway?
🟡percentage yield
🟡atom economy
🟡rate of reaction
🟡usefulness of by products
🟡wether it is a reversible reaction
How do you convert between dm and cm cubed?
Cm^3: dm^3
1000:1
10cm =1dm
How do you calculate the concentration of a solution
Concentration (mol/dm^3 ) = amount in mass/mols➗volume in dm^3
How do you convert between g/dm^3 and mol/dm^3?
➗molar mass
How do you carry out a titration?
🔶biruete clamped using a glass clamp
🔶volumetric pipette to measure alkali
🔶Then put into a conical flask
🔶using a funnel put the acid in the biruette, read the bottom of the minniscous and place the set up on the floor to get at eye level
🔶take out the funnel and add indicator (phenolphthalein)in the conical flask, should be pink
🔶add the acid while swirling when it turns colourless , stop the tap. Repeat 3 times -Dripwise
🔶initial - final = titre
What is the point of a titration?
To find the concentration of the acid or alkali
How do you calculate titration questions?
1) find mols
2) do the stoichemetry
3) convert back to concentration
Mols = volume ✖️concentration
What is the rate of reaction?
How quickly products are formed/reactants used.
Amount of products are formed/reactants used.➗time taken
How do you measure the rate of reaction from a gas syringe? With different concentration
(A conical flask with a rubber bung attached to the gas syringe)
🔹measure a known volume of acid
🔹add known mass of other solute
🔹measure the volume of gas every 30s
🔹repeat with different concentrations of acid
🔹repeat using the same temperature
How do you read a volume time line graph?
At the beginning a steep gradient because more reactant particles means more successful collisions.
A flat line towards the end means that the reaction has stopped.
The gradient measures the rate of reaction
How do you calculate the mean rate of reaction (2 values)?
Do change in y ➗ change in x for
How do you calculate the instantaneous rate of reaction?
At the point draw a tanget.
Then calculate the gradient of this tangent.
How does temperature affect the rate of reaction?
🟡increases rate of reaction as particles hold move more quickly and so would collide more frequently.
🟡 these colliding particles would also have the activation energy or more
🟡therefore leading to successful collisions
Describe the disappearing cross experiment
Draw a black cross on a piece of paper and place beneath a transparent beaker. Place the reactants in the beaker and start timing , stop it when the black cross is no longer visible. Calculate the rate by doing
1➗time
How does increased concentration affect the rate of reaction?
Concentration =how much solute is dissolved in the solvent
🟣 more crowded particles
🟣 more collisions per second
🟣due to rate of collisions increasing , the rate of successful collisions increases
How does increasing pressure affect the rate of reaction?
🟣more particles per unit of volume (in the gas state the particles become more crowded )
🟣more collisions per second
🟣as rate of collisions increases the rate of successful collisions increases
HOw does the size of the reactants affect the rate of reaction.
🟣smaller the pieces, the larger the surface area
🟣more particles are exposed (more reactant particles are available for collisions)
🟣higher frequency of collisions.
🟣due to increased frequency of collisions, there is an increased frequency of successful collisions
How would you use the mass balance experiment to measure the rate of reaction?
NOT WHEN USING HYDROGEN AS TOO LIGHT
Place conical a flask with a cotton wool to avoid spitting on a mass nance and record the mass at regular intervals.
What is the effect of a catalyst on the rate of reaction?
It increases the rate of reaction without using up any of it’s own energy
How do catalysts affect the activation energy?
They provide an alternative reaction pathway , with a lower activation energy. So the particles have enough energy for their collisions to be successful.
A greater proportion of the colliding particles then have the activation energy or more.
What is dynamic equilibrium?
A reversible reaction in a closed system, when the rate of the forward reaction is equal to the rate of the reverse reaction.
The concentration of the reactants an products must be stable.
What is a reversible reaction?
A reaction where the products of the reaction can react to produce the original reactants.
What does a ‘shift in the position of equilibrium’ mean?
The side to where it shifts has a larger percentage yield (more is made).
Eg: a shift to the left makes more reactants
A shift to the right makes more products
How does pressure change the position of Equilibrium?
Increasing the pressure will cause a shift to the side with less GAS mols. Because a higher pressure means less area.
How does temperature shift the position the equilibrium ?
Then through Le chatilers principal, the system will try to counteract this change as it wants to go back to before.
If there is an increase in temperature.
The system will want to get rid of this extra heat and so will perform an endothermic reaction, as it absorbs heat from the surroundings.
How does concentration shift the position of equilibrium?
Then through Le chatilers principal, the system will try to counteract this change as it wants to go back to
If the concentration of a substance has been increased then the position of equilibrium will be moved to the opposite side away from it.
What effect do catalyst have on the position of equilibrium ?
They don’t have any effect. They only increase the rate and make it a more efficient process
Why might a manufacturer compromise on temperature?
Cannot make to low because of activation energy and rate of reaction.
Cannot make too high because it’s expensive
Why might a manufacturer compromise on pressure ?
High pressure requires tough reaction vessels which can be quiet expensive
Low pressure is cheaper to generate
What are concordat titres?
Titres that are within 0.1of each other
When do gases occupy the same volume?
When they are all at room temperature and pressure
How do you handle gas calculations?
Volume = 24 (concentration) ✖️mols
Why do to measure the bottom of a minniscous ?
To avoid a parallax error
Why are indicators such as phenolphthalein used?
There is a sudden colour change as opposed to a gradual change
Why should industrial process have the highest atom economy possible?
To the reduce the production of unwanted products.
To make the process more sustainable
What does it mean for the particles to have successful collisions?
The particles have the activation energy
What is the cotton wool used for in the mass scale rate of reaction experiment?
The cotton wool prevents spitting. BUT allows the gases to escape from the flask , no worry
How could titrations be improved
🔵swirling flask, ensures mixing
🔵use a white tile underneath to see end point clearly
🔵 add drop-wise, to see colour change in one drop
How do data loggers and ph probes affect titrations?
They are more accurate as you can predict the endpoint more accurately
What is the very first titration results accounted for?
They are seen as a rough test, more of an anomaly and are not used in the results data
How does surface area affect rate of reaction?
The higher the SA the higher the rate of reaction
What is the reading on this burette?
0.65 cm3
Calculate concentration
Define Le chatilers principle
“When a change is made to the reaction at equilibrium, the position of equilibrium moves to oppose the change”
What is another way of calculating the rate of reaction from just time
1/ time is directly proportional to the rate
